The intake of the air/fuel mixture and the exhaust of burned gases must be carefully controlled for proper operation of an internal combustion engine. This function is carried out by components associated with the engine's cylinder head and are referred to as the valve train. These components typically include the valves, springs, rocker arms, camshaft, lifters and pushrods among others and are generally located in the cylinder head of the engine.
Generally, as the camshaft rotates, a camshaft lobes pushes against a lifter which, in turn, either directly or through the use of a pushrod, pushes one side of the rocker arm causing the rocker arm to rotate about a mounting pin. The other side of the rocker arm, in turn, pushes on the valve stem allowing the air/fuel mixture and/or exhaust to enter and/or leave the combustion chamber, respectively. As the camshaft continues to rotate, the pushrod follows the curve of the camshaft due to the valve spring force and returns to its initial position. This allows the rocker arm, biased by the valve spring, to rotate in the opposite direction thereby closing the valve to the combustion chamber. This arrangement of components has no means of compensating for slack due to wear of the components in the valve train which, in turn, causes increased wear and noise.
To overcome this, prior art arrangements make use of a hydraulic lash adjuster located between the camshaft and pushrod. Other prior art systems, typically in the case of an overhead camshaft, locate the hydraulic lash adjuster in the rocker arm. The disadvantage to such placement of the hydraulic lash adjuster is that the lash adjuster moves linearly. Because the hydraulic lash adjuster is generally the heaviest component in the valve train, by placing the hydraulic lash adjuster in rocking motion (about the rocker arm's axis of rotation) instead of linear (along the pushrod axis), as in prior art arrangements, the effective valve train mass is reduced thereby reducing valve spring load and valve train friction and reducing hydraulic lash adjuster wear.